In the foundry industry, one of the processes used for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry mix which is a mixture of sand and an organic or inorganic binder.
One of the processes used in sand casting for making molds and cores is the no-bake process. In this process, a foundry aggregate, binder, and liquid curing catalyst are mixed and compacted to produce a cured mold and/or core. In the no-bake process, it is important to formulate a foundry mix which will provide sufficient worktime to allow shaping. Worktime is the time between when mixing begins and when the mixture can no longer be effectively shaped to fill a mold or core.
A binder commonly used in the no-bake process is a polyurethane binder derived by curing a polyurethane-forming binder with a liquid tertiary amine catalyst. Such polyurethane-forming binders used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1370.degree. C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 815.degree. C.
The polyurethane-forming binder usually consists of a phenolic resin component and polyisocyanate component which are mixed with sand prior to compacting and curing. Both the phenolic resin component and polyisocyanate component generally contain a substantial amount of organic solvent which can be obnoxious to smell and can create stress for the environment such as smoke when the binder is cured. Because of this, there is an interest in developing binders which do not require the use of organic solvents.
U.S. Pat. No. 5,455,287 discloses no-bake foundry mixes where the binder comprises (a) polyether polyol having a hydroxyl number between 200-600 and a viscosity of 100-1000 centipoise at 25.degree. C., (b) an organic polyisocyanate component, and (c) a liquid tertiary amine catalyst, preferably a bicyclic tertiary amine.